This invention relates to a novel multipurpose lubricating grease composition having particularly desirable high temperature properties. More particularly, this invention involves a lubricating grease composition comprising a lubricating base oil and an effective amount of a selected pyrrolidone compound as the grease thickener.
A wide variety of thickening agents for greases have been developed over the years including the alkali salts of fatty acids, clays, polyureas, asbestos, carbon black, silica gels, aluminum complexes, polymers, phthalocyanine, indanthrene, etc. Despite the number and wide variety of such thickeners, over 90 percent of worldwide grease production uses alkali metal soaps as the thickening agent. The only nonsoap thickeners which have achieved commercial importance are the aluminum complexes, clays and polyureas and then only to a very limited extent.
The soap thickeners which have been mainly used are derived from the saponification of fats and oils by lithium and calcium hydroxides, although the sodium and barium soaps have been used in smaller amounts for special applications. The fats and oils are mostly mixtures of C.sub.16 and C.sub.18 fatty acid precursors with the preferred soap being lithium 12-hydroxystearate. This preferred lithium soap thickener constitutes over 50 percent of all greases and most all premium multipurpose greases. The lithium soap greases are described and exemplified in many patents including U.S. Pat. No. 3,758,407 issued to G. L. Harting on Sept. 11, 1973; U.S. Pat. No. 3,791,973 issued to S. Gilani et al on Feb. 12, 1974; and U.S. Pat. No. 3,929,651 issued to D. Murray et al on Dec. 30, 1975.
While a variety of thickeners have been developed, as noted above, they generally do not give equivalent performance to lithium 12-hydroxystearate, particularly in the critical areas of high temperature application, shear stability, water resistance and additive compatibility.
Although 12-hydroxystearic acid is the most desirable fatty acid grease thickening component, it does have some supply and economic problems associated with it and lithium, although readily available in many parts of the world, is expensive.
Accordingly, it is desired to develop a new grease thickener system that eliminates dependence on 12-hydroxystearic acid and reduces or eliminates lithium usage.